Ce3⁺- and Cu2⁺-modified chitosan were developed as sustainable bio-based adsorbents for thiophene removal from a model fuel. Structural analysis showed that Ce3⁺ preserved chitosan crystallinity, while Cu2⁺ induced partial amorphization. Ce-chitosan achieved a higher adsorption capacity (13.82 mg S·g−1) than Cu-chitosan (9.94 mg S·g−1), with kinetics following a pseudo-second-order model. Thermodynamic analysis revealed a large negative enthalpy change (–136.9 kJ·mol−1) for Ce-chitosan, confirming an exothermic chemisorption process, whereas Cu-chitosan exhibited less favorable energetics. Ce-chitosan also retained 88.9% of its capacity in the presence of competing heterocycles and 77.6% after five regeneration cycles, highlighting its efficiency, selectivity, and reusability. These findings establish Ce-chitosan as a promising green adsorbent for sustainable fuel desulfurization.
